Cathode-ray deflection circuit



July 9, 1946. A. v. BEDFORD 2,403,487

CATHODE RAY DEFLECTION CIRCUIT Filed July 50, 1941 21 1l J4l MII" -Iwlll--lllllll nventor Alda, zedford 8B .y l

Y (Ittomeg l Patented July 9, 1946 oFFica cA'rHonE-nsr DaFLEc'noN omctn'r Aida V. Bedford, Collingswood, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application July an, 194i, serial No. 404.613

s claims. (ci. sis-21) 1 My invention relates to cathode ray deilection circuits and particularly to circuits employing electromagnetic deiiection.

One of the more diicult problems in designing a deflecting circuit is that of obtaining the desired deecting current wave shape'. It is especially difiicult in cases where the defecting coils have a substantial amount of. distributed capacity and where either the deilecting coil resistance itself, or the coil resistance together with lilehresistance of a cable or the like, is rather 8 An object of the present invention is to provide an improved method of and means for producing a ow of deflecting current of the desired wave shape.

A further object oi the invention is to provide an improved electromagnetic deiiecting circuit for use with deilecting coils having `a substantial amount of resistnce and distributed capacity.

A still further object 'of the invention isv to provide an improved deiiecting circuit for passing a sawtooth current through deecting coils having a substantial amount of resistance eiectively 'in series therewith and a substantial amount of capacity effectively in shunt thereto.

In one embodiment of the invention. a vspecial network preceding the deecting circuitl output tube adds voltages from two circuit branches to supply to the grid of this tube (l) a voltage that would give the desired sawtooth current in the absence of capacity across the deiiect-ing coil and (2) an additional voltage that supplies the current taken by the capacity, this additional voltage being given a wave shape which takes into consideration the deecting coil resistance and/or cable resistance or the like in series with the coil.

In a preferred embodiment, there is a network preceding the output tube which simulates the output circuit of said tube, this network including a condenser corresponding to distributed capacity and being itself preceded by a wave shaping means for producing current of the proper wave shape through the said network.

The invention will be better understood from the following description 'taken in connection with the accompanying drawing, in which Fig. 1 is a circuit diagram of a deiiecting circuit embodying my invention,

Fig. 2 is a diagram of an equivalent'circuit for a portion of the circuit in Fig. 1, and

Fig. 3 is a circuit diagram of a preferred embodiment of the invention.

Corresponding parts in the several iigures are indicated by like reference characters.

. 2 Referring to Fig. 1, the invention is shown applied to a cathode ray deilecting circuit comprising deiiecting coils I0 which are supplied through a cable I2 withdeilecting current from an output tube I I. The output circuit of tube II may include a conventional choke coil I3 and blocking condenser Il.

vOne oi' the voltage wave components applied to the grid ofthe output tube II consists of the.

sistor I8 and is discharged rapidly through a' discharge tube I.'l in responsel to the application oi'a positive pulse I8 to the grid thereof..

The pulses I8 may be supplied to the discharge tube I1 from any suitablejsource s uch as a blocking oscillator indicated at I0.

The combined sawtooth-puise wave across C-R is impressed across a potentiometer circuit comprising a blocking condenser vCI- and the resistors R2 and R3, all connected in series. The voltage across resistor R2, which has 4a low resistance compared with that oi' R2, is applied to the grid of the output tube llvthrough the usual coupling condenser 2|. The potentiometer circuit does not appreciably load the capacitor C since the resistance of R2 is made great enough to give R2-C a time constant that is long compared with a deflection cycle.

In accordance with my invention, another volt-- age wave is added to the above-mentioned sawtooth-pulse wave by means of a condenser C3' E te:

where C is the capacity of condenser Cl and E v is the voltage across C2and R.

The circuit operation will be understood by referring to Fig. 2 where Rip represents the cathode-plate resistance of the output tube II, R4 represents the deecting coil resistance and any other resistance in series therewith, such as all or part of the resistance of the cable I2, L represents the inductance of the delectlng coils I0, and Cd represents the distributed capacity of the coils l and any additional capacity across them such as the capacity of the cable I2.

The circuit operation of Fig. 1 may be analyzed as follows:

The combined sawtooth-pulse voltage across C-R consists of a sawtooth voltage across Cl, another sawtooth voltage across C2 and a pulse voltage across R. The voltages across CI and C2v are those required to drive a sawtooth current through Rp and through R4, respectively, and thev voltage across R is that required to drive a sawtooth currentthrough the inductance L. No other voltage at the grid of tube I would be required if the distributed capacity Cd were absent.

However, there is the capacity Cd across R4 and L which will draw current. I provide this current by the additional differentiated voltage obtained by the circuit C3-R3 -connected across C24-R. It will be apparent that the voltage across C2-R is a sawtooth wave plus a pulse, just as the voltage across R4 and L is a sawtooth wave plus a pulse. Therefore, the differentiated voltage appearing across R3 is the voltage required to supply current to the distributed capacity Cd for the assumed desired condition of a straight or undistorted sawtooth current owing through the inductance L, that is, through the deiiecting coils I0.

It may be noted that the operation of that por- -tion of the above circuit for supplying the capacity. current for Cd is based on the assumption that thel output tube feeds into a pure resistive load so far as the grid voltage vs. plate current characteristic is concerned. This assumption, of course, is not strictly true.

Fig. 3 shows a preferred embodiment of the invention which corrects more exactly for the capacity across the deflecting coils I0. In the output circuit of the tube I'I there is a condenser 3| across which a sawtooth Voltage appears and a resistor 32 across which a pulse voltage appears.

'A potentiometer comprising resistors 33 and 34 is connected across condenser 3|, and the input electrodes of an amplifier tube 35 are connected across resistor 34.

The combined sawtooth' and pulse voltage appearing across the condenser 3| and the resistor 32 is diierentiated in a circuit comprising a condenser 31 and the resistor 34. This differentiated voltage is added in the resistor 34 to the sawtooth voltage whereby the combined voltage Wave is impressed upon the grid of amplifier 36.

In th'e plate circuit of amplifier 36 there is a network which simulates the output circuit of the output tube Il, this output circuit being shown in equivalent form in Fig. 2. The network comprises a resistor 38 corresponding to Rp (Fig. 2), a resistor 39 corresponding to R4, an inductance coil d0 corresponding to theinductance L of coils I0, and a condenser 4I corresponding to distributed capacity Cd. The tube 36 is of a. type having such high plate impedance with respect to its plate circuit that the plate current is closely proportional to the grid voltage. As will be explained, the voltage appearing across this network is the Voltage which, when applied to th'e grid of the output tube II will produce current through the deiiecting coils that is a straight sawtooth.

The network voltage is applied to the grid of tube I! through an amplifier 42 for reversing `its polarity, it being preferred that the tube be driven towards plate current cutoii? during the return-line time as is well known in the art. The tube II functions, however, as a substantially linear amplifier.

Considering the function of the above-described network more in detail, it will be apparent that the sawtooth voltage component applied to the grid of tube v33 produces a voltage pulse across coil 40 and a voltage sawtooth across the resistors 38 and 39. In the absence of capacity across the deflecting coils this would produce a straight sawtooth current in the deflecting coils.

The value of the resistor 32 with respect to the condenser 3| is such that the voltage wave applied to the differentiating condenser 31, is the same shape as the voltage which would exist across Cd, when a straight sawtooth current ows through R11 and L. Hence, the current through condenser 31 corresponds to the current through Cd and generates a component of IR drop in resistor 34 which causes a similar component of current to ow into the network 38, 39, 4D and 4|. The ow of this component of current then results in a voltage component being applied to th'e grid of tube 42 (and then to the grid of tube II) which is correct to cause tube II to supply the desired capacity component of current to its actual output circuit. Therefore, the voltage appearing across the network 38, 39, 40 and 4| when applied to the grid of the output tube causes th'e desired undistorted sawtoothl current to iiow through the deflecting coils.

I claim as my invention:

1. A cathode ray delecting circuit comprising deflecting coils having distributed capacity thereacross and having resistance effectively in series therewith, a vacuum tube having a grid circuit and having a-plate circuit coupled to said coils to supply defiecting current therethrough, a capacitor and a resistor .in series, means -for producing a sawtooth voltage wave across said capacitor and a Voltage pulse across said resistor, means comprising a branch circuit connected across said capacitor and resistor for differentin ating the voltage appearing across said resistor and at least a portion of the voltage appearing across said capacitor, means for adding said differentiated voltage to at least a portion of the voltage appearing across said capacitor, and means for impressing said added voltages upon said grid circuit.

2. A cathode ray deecting circuit comprising deilecting coils having distributed capacity thereacross and having resistance eiectively in series therewith, a vacuum tube having a grid circuit and having a plate circuit cou-pled to said coils to supply deecting current therethrough, a plurality of condensers in series with a peaking resistor, means for producing a sawtooth voltage wave across each of condensers and a voltage `pulse across said peaking resistor, means for differentiating the voltage appearing across said resistor and across at least one but not all of said condensers, means for adding said diierentiated voltage to the voltage appearing across said peaking resistor and said plurality of condensers, and means for impressing said added voltages upon said grid circuit.

3. A cathode ray deflecting circuit comprising deflecting coils having distributed capacity thereacross and having resistance effectively in series therewith, an output tube coupled to said coils to 5 supply deflecting current therethrough, a plurality of amplifier tubes connected in cascade with said output tube, each of said amplier tubes having a, grid circuit and a plate circuit, a network in the plate circuit, of one of lsaid tubes which simulates the output circuit of said output tube, said network comprising an inductance coil and a resistor in series, both shunted by a condenser representing said distributed capacity to form a parallel combination of elements, and a resistor connected in series with said parallel combination, and means for applying to the grid of said one tube a voltage consisting of a sawtooth component and a component which is a derivative of said sawtooth component and of a voltage pulse.

4. A cathode ray deflecting circuit comprising deflecting coils having distributed capacity thereacross and having resistance eie'ctively in series therewith, an output tube coupled to said coils to supply deecting current therethrough, a plurality of amplier tubes connected in cascade with said output tube, each of said amplifier tubes having a grid circuit and a plate circuit,.a network in the plate circuit of one of said tubes which simulates the output circuit of said output tube, said network comprising an inductance coil representing deilecting coil inductance and a resistor in series representing said resistance effectively in series, both shunted by a. condenser representing said distributed capacity to form a parallel combination of elements, and a resistor representing the plate-cathode resistance of said output tube connected in series with said parallel combination, said network having an impedance which is proportional to the impedance of the load circuit of said output tube, said load circuit including the .plate-cathode resistance of the output tube; and means for applying to the grid of said one tube a voltage consisting of a sawtooth component and a component which is a derivative of said sawtooth component and of a voltage pulse.

5. A cathode ray deflecting circuit comprising deiectingV coils having' distributed capacity thereacross and having resistance `effectively in series therewith, an output tube coupled to said coils to supply deflect-ing current therethrough, a plurality of amplifier tubes connected in cascade with said output tube, each of said amplifier tubes having a grid circuit and a plate circuit, a network in the plate circuit of one of said tubes which simulates the output circuit of said output tube, said network comprising an inductance coilrepresenttooth component for producing the voltage drop across said inductance. coil and a component which is a derivative of said'sawtooth component and of a, voltage pulse.

6. The invention according to claim 5 wherein saidlast means comprises a resistor and acondenser in series and means for lproducing a sawtooth voltage across said condenser and a pulse voltage across said last resistor, means for ob` taining a derivative of the voltages appearing l tube.

across said last mentioned series combination of resistor and condenser, and means for vadding said last sawtooth voltage and said derivative voltage and applying them to the grid of said one ALDA v, BEDFoRn. 

